This invention relates to durable transparent ceramic compounds. There is a need for these compounds in applications requiring substantial transmission and imaging capabilities in the visible range and the infrared range. These requirements can be found in both military and commercial applications. For example, infrared transparent domes are needed for missiles and transparent envelopes are needed in different types of vapor lamps. Many transparent materials are not adequately durable for these applications, thus, the search has been directed towards developing transparent ceramics. Although many ceramic compounds satisfy the durability requirement, they are not transparent to a sufficient degree for these applications. For instance, alumina is a very hard material but the main problem is that it is not sufficiently transparent and scatters light to an excessive degree. An additional consideration for a candidate material in the cost of manufacturing, thus, methods that require individual processing of these windows are bound to remain an unfeasible alternative from a cost point of view. From this perspective, forgoing and hot-pressing methods are not desirable. This leaves batch processing methods as a desirable feasible alternative and sintering lends itself to the manufacture of a plurality of units in a single run. However, the sintering of transparent ceramics is not widely known or practiced.
Aluminum oxynitride is a promising candidate for applications requiring multi-spectral transmission capabilities. The only known prior attempt at producing a sintered aluminum oxynitride body is found in U.S. Pat. No. 4,241,000, wherein precursor powders are mixed and the sintering step is used to both react and sinter the precursor powders to produce an aluminum oxynitride body. As described therein, the maximum density obtained for the sintered body was 97.2% of theoretical density. The problem is that the resulting material is not sufficiently transparent for the applications mentioned hereinabove.